RFID Systems
Radio frequency identification (“RFID”) tags may be manufactured as passive, active, or battery assisted passive (“BAP”) devices. Active tags have on-board batteries and periodically transmit their ID signals without interrogation, whereas a battery-assisted passive device may have a small battery on board and is activated when interrogated by an RFID reader. Conventionally passive tags are less expensive and smaller because there is no battery.
In conventional systems passive RFID must be interrogated (or illuminated) with a power level roughly three magnitudes stronger than the desired output signal to initiate operation of the device. The strength of the desired output signal is important for managing interference in certain environments; therefore battery assistance may be crucial in certain applications.
For specific identification purposes, the tags may either be read-only, have a factory-assigned serial number, or they may be read/write, where a unique ID may be written into the tag by a user. Field programmable tags may have the ability to be written to once and then read multiple times.
RFID tag systems conventionally contain at least two parts: an integrated circuit for processing a radio-frequency (RF) signal and an antenna for receiving and transmitting the signal. In operation an RFID reader transmits an encoded radio signal to interrogate the tag. The RFID tag receives the message and then responds with its identification and other information. The responses range from simply a unique tag serial number to product-related information such as a stock number, lot or batch number, production date, or other specific information.
RFID tag systems may operate in a wide RF range, with several designated frequency ranges set aside for RFID operation across the radio spectrum. For example and without limitation, RFID tags for tracking animals often operate in the 120-150 KHz range while microwave versions of RFID systems can be found in WLAN or Bluetooth operations.
Power Generation
Mechanical energy is manifested in the bodies of humans and animals as a result of their physical processes. Such physical processes include both voluntary and involuntary muscle movements. It is sometimes desirable to convert mechanical energy to electrical energy. An example is the conversion of kinetic energy into electrical energy as the kinetic energy of a mass moves in a magnetic field relative to a conductive coil thereby converting the kinetic energy of the mass to electrical energy by through electromagnetic induction. A magnet moving axially through the center of a coil will induce a voltage across the coil terminals. The voltage is induced because it is the result of the changing magnetic flux on the coil.
One conventional application of this is in shaker flashlights, where the flashlight is vigorously shaken back and forth, causing a magnet to move through a multi-turn coil, which provides charge to a battery. The exact amount of power derived from this system will depend on the characteristics of the coil and magnet and together with the amount of motion induced onto the system.